Overall, the design and manufacture of a functional, robust, and durable joint prosthesis is a complex and multifaceted problem involving anatomical, biocompatibility, biomechanical, and surgical considerations. From a functional perspective, mechanical design considerations should address the joint range of motion, center of rotation, force-transmission-capabilities, and wear resistance of the component. Anatomical issues for consideration involve the shape of the intramedullary stem and of the articulating surface, and the need for a range of sizes to accommodate anthropomorphic variations. Surgical concerns should take into account the need for appropriate instrumentation utilized during the implantation procedure to facilitate an accurate osteotomy, effect minimal bone removal, and preserve surrounding soft tissues. The design objective for such an implant to replace the distal articular surface of a diseased and/or damaged CMC joint should be to relieve pain, allow maximum range of motion, and restore to the patient a high degree of hand functionality. Size and geometric features of the component are in a large way dictated by morphometric measurements of the natural CMC joint; however, the ultimate component should be such that it will exhibit longevity when subjected to rigorous and demanding anatomically relevant constraint and loading situations.
There have been a number of complete CMC joint implants wherein implants described and marketed having articulating surfaces have been surgically inserted into both the base of the first metacarpal and the trapezium. Examples of these are found in U.S. Pat. Nos. 4,276,660; 4,955,916; 5,645,605; and 5,702,469. Other alternatives include replacing the entire trapezium, either along with the base of the metacarpus (see U.S. Patent Publication No. 2005/0251625) or by itself (see U.S. Patent Publication 2007/0021839). Still other alternatives which constitute hemi joint replacements include the various prior art implants described in U.S. Pat. No. 7,182,787 and the implant described in U.S. Patent Publication 2005/0033426.
Despite the wide variety of prospective solutions to the all too frequently occurring problem of a deteriorated joint at the base of the thumb metacarpus, the search has continued for still further, even more improved solutions for hemi joint replacement.